Attic Air Sealing
Insulation slows heat. It does not stop air. Warm air from your living space escapes through dozens of hidden gaps in the ceiling, carrying heat and moisture into the attic. Sealing those gaps before new insulation goes in is often the single most cost-effective energy fix in an older house, and it is the main defense against attic condensation.
Where the leaks are
- Top plates — the tops of interior walls, often open along their whole length in older framing
- Plumbing vent stacks and the oversized holes cut around them
- Electrical penetrations, junction boxes and ceiling fan boxes
- Recessed can lights, especially older non-airtight models
- Chimney and flue chases — the open gap between the chimney and the framing
- Duct boots and register openings in the ceiling
- Dropped soffits over kitchen cabinets and bathtubs, which are often open to the attic
- The attic hatch itself, usually unsealed and uninsulated
- Split-level and knee-wall transitions, where an attic meets a wall cavity
How we seal
| Gap | Material |
|---|---|
| Small holes around wires and pipes | Fire-rated sealant or low-expansion foam |
| Large openings, dropped soffits, chases | Rigid foam board or drywall cut to fit, sealed at edges |
| Gaps around chimneys and flues | Sheet metal and high-temperature sealant (no foam near heat) |
| Older recessed lights | Airtight IC-rated covers or replacement with sealed LED retrofits |
| Attic hatch | Weatherstripping and a rigid insulated cover |
Fire safety governs the materials near heat sources. Combustible materials keep the clearances the appliance manufacturer and code require.
What sealing changes
Homes we seal typically become noticeably less drafty, upstairs rooms hold temperature better, and the attic stays drier in winter because less house air reaches the roof deck. When a blower door test is part of the job, the report shows the leakage before and after.
Ventilation and combustion safety
A tighter house moves less air on its own. If you have a gas water heater or furnace that draws combustion air from the house, or no working bath and kitchen exhaust, sealing can change how those systems behave. We check for atmospheric-vented appliances during the inspection. When one is present, we recommend a combustion safety check by an HVAC technician after the work.
Air sealing price ranges
| Home | Typical air sealing cost |
|---|---|
| Simple rambler, open attic | $1,200 – $2,000 |
| Two-story or split-level | $1,800 – $2,800 |
| Older home with chases, soffits and many can lights | $2,500 – $3,500 |
Air sealing is included in our attic insulation proposals by default. If the attic already has good insulation, we can pull it back in sections, seal and replace it.
Air sealing questions
Can you air seal over existing insulation?
Not effectively. The gaps are at the ceiling, under the insulation. Sealing is easiest when the attic is empty, which is why it pairs so well with insulation removal.
Will my house become too tight?
Older houses in our area are far from too tight. Sealing the attic floor brings them closer to typical new-construction levels, not past them. Working exhaust fans in bathrooms and the kitchen handle moisture from cooking and showers.